Temperature dependence of resistance and thermopower of thin indium tin oxide films

We have measured the resistance and thermopower of a series of RF sputtered and annealed indium tin oxide (ITO) thin films from 300 K down to liquid-helium temperatures. Thermal annealing was performed to modulate the levels of disorder (i.e., resistivity) of the samples. The measured resistances are well described by the Bloch-Grüneisen law between 150 and 300 K, suggesting that our thin films are metallic. At lower temperatures, a resistance rise with decreasing temperature was observed, which can be quantitatively ascribed to the two-dimensional electron-electron interaction and weak-localization effects. The thermopowers in all samples are negative and reveal fairly linear temperature dependence over the whole measurement temperature range, strongly indicating free-electron like conduction characteristics in ITO thin films. As a result, the carrier concentration in each film can be reliably determined. This work demonstrates that ITO films as thin as 15 nm thick can already possess high metallic conductivity.